1. Field of the Invention
The present invention relates to a clamping apparatus adapted to clamp an object to be clamped or fixed (referred to as a clamped object hereinafter) such as a metal mould, a work pallet and the like onto a fixed table of a process machine such as an injection moulding machine, a machining center and so on, and more specifically to a clamping apparatus of the type including a clamping-member actuated straightly along an axis declining in a forward downward direction relative to a clamped surface of a clamped object placed in front of the clamping apparatus.
2. Description of Prior Art
Such a prior clamping apparatus is described in Japanese Patent Publication No. 52-30371 and Japanese Utility Model Publication No. 55-1861. According to each prior art, a clamping end surface of a clamping-member is adapted to be directly brought into contact with a clamped surface of a metal mould.
According to the aforementioned kind of clamping apparatus, at the end of the clamping actuation a small dynamical friction force takes effect between both the clamped surface of the metal mould and the clamping end surface of the clamping-member, and at the beginning of the unclamping actuation a large statical friction force takes effect between both those surfaces.
In order to prevent an obstruction to an unclamping actuation of the clamping apparatus from being caused by the large statical friction force, conventionally it is required to make the unclamping actuation force of the clamping apparatus stronger. As a result, the clamping apparatus becomes larger in size.
In order to attain a downsizing of the clamping apparatus, the inventors of the present invention proposed the following previous to the filing of the present invention. That is, a coefficient of friction between the clamped surface of the metal mould and the clamping end surface of the clamping-member was made smaller by covering the surface of the clamping-member with a sliding enhancement material such as a coating, a lubricant and the like so as to allow a reduction of the unclamping actuation force.
But, since such a sliding enhancement material tends to stick to the metal mould to be replaced and then removed thereby, its service life is extremely short, so that an improvement is required for ensuring the unclamping actuation of the hydraulic clamp.
Further, usually a finished accuracy of the clamped surface of the metal mould is different in the respective metal moulds to be replaced. In the case of a bad finished accuracy of the clamped surface, since a layer of the sliding enhancement material is readily broken, both the clamped surface and the clamping end surface tend to cause local seizures. As a result, it is apprehended that a coefficient of friction between both those becomes larger gradually and finally the clamping apparatus becomes incapable of effecting its unclamping actuation.
On the other hand, a technology for allowing the reduction of the unclamping actuation force, which has a basic construction different from that of the clamping apparatus with the inclined direct operated clamping-member according to the present invention, is described in U.S. Pat. No. 4,932,640 previously proposed by one of the inventors of the present invention. It employs a sliding member interposed between a wedge supporting surface formed in a housing of a wedge force-multification type hydraulic clamp and a sliding contact surface of a tightening wedge. But, since this wedge force-multification type hydraulic clamp is constructed so as to clamp a clamped object by means of a swinging actuation of its clamping-member, it doesn't suffer an abuse of abnormally increasing the coefficient of friction between the clamped object and the clamping-member.